The present invention relates to an apparatus, system, and method for dispensing fluids into containers and, more particularly, to an improved mechanism for cleaning fluid dispensers associated with such apparatus, system, and method. The invention also relates to a film from which the containers can be made and which also facilitates the cleaning of the dispensers.
The invention finds particularly utility in the field of foam-in-place packaging, which is a highly useful technique for on-demand protection of packaged objects. In its most basic form, foam-in-place packaging comprises injecting foamable compositions from a dispenser into a container that holds an object to be cushioned. Typically, the object is wrapped in plastic to keep it from direct contact with the rising (expanding) foam. As the foam rises, it expands into the remaining space between the object and its container (e.g. a corrugated board box) thus forming a custom cushion for the object.
A common foamable composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure, i.e., a polyurethane foam, which serves to protect the packaged object.
In other types of foam-in-place packaging, an automated device produces flexible bags from flexible, plastic film and dispenses a foamable composition into the bags as the bags are being formed. As the composition expands into a foam within the bag, the bag is sealed shut and typically dropped into a container holding the object to be cushioned. The rising foam again tends to expand into the available space, but does so inside the bag. Because the bags are formed of flexible plastic, they form individual custom foam cushions around the packaged objects. Exemplary devices are assigned to the assignee of the present invention, and are illustrated, for example, in U.S. Pat. Nos. 4,800,708, 4,854,109, 5,376,219, and 6,003,288, the contents of each of which are incorporated entirely herein by reference.
One problem with the foamable compositions used to make polyurethane foam for foam-in-place packaging is that the foam precursors and resultant foam tend to have somewhat adhesive properties. As a result, the foamable composition tends to stick to objects that it strikes and then hardens into foam. One location where this causes a particular problem is the discharge nozzle of the dispenser from which the foam precursors are ejected. As is known, the polyol and isocyanate foam precursors must be withheld from mixing with one another until just prior to injection. In the most common type of dispenser, the two foam precursors enter the dispenser, mix with one another, and then exit the dispenser via the discharge nozzle as the foamable composition. As the dispenser operates over and over again, particularly in automated or successive fashion, foamable composition tends to build up around the discharge port of the dispenser, harden into foam, and block the proper exiting of further foamable composition. As a result, the discharge nozzle and discharge port must be frequently cleaned to ensure continued operation of the dispenser.
A number of cleaning solutions have been proposed. One such solution employs a solvent that is capable of dissolving the foamable composition. Such solvent is continually pumped into the dispenser and through the discharge port to carry away any residual foamable composition remaining on or around the discharge port. While this solution has proven to be somewhat effective, the discharge port nevertheless eventually becomes occluded with foam, requiring the dispenser to be disassembled and cleaned. Furthermore, the solvent adds to the expense and complexity of the foam-in-place packaging machinery.
Another solution is to employ a solvent-soaked pad on which to wipe the face of the discharge nozzle in order to remove residual foamable composition therefrom, e.g., as disclosed in U.S. Pat. No. 4,674,268. While this solution has also been shown to be somewhat effective, it entails a rather complex mechanized system for moving the dispenser into contact with the wiping pad, thereby adding expense, complication, and potential for mechanical problems to the foam-in-place system in which it is incorporated. Additionally, the wiping pad frequently becomes fouled with the precursors and foam, necessitating continuous monitoring and replacement of the pad. As can be appreciated, such limitations are not conducive to an automated foam-in-place packaging process.
A further solution to the problem of dispenser cleaning is the use of two discharge nozzles to dispense separately the polyol and isocyanate foam precursors into a bag, wherein the two precursors are mixed. Although this arrangement avoids the mixing of the two precursors in a single dispenser, and therefore also avoids the formation of foam on and around the discharge port of the dispensers, the need to periodically clean the discharge nozzles remains. This is particularly true for the nozzle used to dispense the isocyanate precursor because the isocyanate reacts with moisture in the air to crystallize at the discharge port of the nozzle. Thus, some method for cleaning such a dual nozzle dispenser must still be employed.
Accordingly, a need exists in the art for an improved means for automatically cleaning dispensers used in foam-in-place packaging.